Conventional valves having a sealing element movable axially into and out of engagement with a stationary seat on the valve body by rotating the valve stem are well known in the art, as disclosed for example in U.S. Pat. No. 4,556,196. The seal in the annulus between the valve stem and bonnet typically provides the seal along the valve stem, while another seal axially positioned between the valve body/bonnet threads and the valve seating element provides the valve body/bonnet seal. These valves are well suited for numerous applications, and have been widely accepted in various industries.
For certain applications, however, a valve having an outside yoke and seal (an OS&Y valve) may be preferred. In an OS&Y valve, the valve stem seal is held in place by an assembly external of the valve body and bonnet base, and accordingly the valve stem seal may be tightened or replaced without disturbing the valve body/bonnet base connection. OS&Y valves are also well known in the art, as typified by the AGCO M5Y Gauge Valves.
A significant deterent to the further acceptance of OS&Y valves relates to their high manufacturing costs. OS&Y valves are typically fabricated from a specially constructed valve body, so that a reliable connection can be effected between the valve body and the bonnet base. Another disadvantage of prior art OS&Y valves is the poor reliability of the thermoplastic seal between the valve body and the bonnet base.
The disadvantages of the prior art are overcome by the present invention, and techniques are hereinafter disclosed for forming an improved OS&Y valve which achieves high reliability and comparatively low manufacturing costs.